Pressure vessel for storing an insulating mixture for an electrical transformer and associated process

Abstract

A pressure drum (1) for storing an insulating mixture (M) for an electrical transformer, the pressure drum (1) comprising a chamber (2) configured to receive the insulating mixture (2), the chamber comprising a wall (20) defining an internal volume (21), a heating device (3) comprising at least one electric heating element (4) positioned within the chamber (2), the heating device (3) being configured to internally heat the insulating mixture (M) to make it homogenized and allow the electrical transformer to be filled. Abstract figure: Figure 3

Description

Title of the invention: Pressure drum for storing an insulating mixture for an electrical transformer and associated method technical field

[0001] The present invention relates to the field of electrical transformer insulation, more specifically to the field of gas-based electrical insulation of electrical transformers.

[0002] An electrical transformer allows the voltage of the electrical network to be adapted to make the electrical current usable. An electrical transformer thus accommodates very high and potentially lethal electrical voltages if an operator gets too close to the transformer's wires. It is therefore essential to electrically insulate the electrical transformer with an insulator.

[0003] In the prior art, electrical transformers and other high-voltage equipment were insulated with a gas comprising sulfur hexafluoride (SF6), which has excellent insulating and arc-interrupting properties. However, such a gas has a very high global warming potential (GWP), and alternative gases have been sought.

[0004] It is known to insulate an electrical transformer using an insulating mixture of gases comprising several components, in particular, fluoronitrile (C4-F7N), oxygen (O2), and carbon dioxide (CO2) or nitrogen (N2). In practice, the components must be in precise proportions to exhibit properties that allow for satisfactory electrical insulation of the electrical transformer.

[0005] The insulating mixture is prepared in a chemical plant and packaged directly into pressurized drums for storage, transport, and filling of electrical transformers. This packaging is carried out in liquid phase for logistical cost reasons.

[0006] In practice, it is not possible to directly recharge an electrical transformer by connecting a pressure drum to the electrical transformer. Indeed, in the pressure drum at ambient temperature, the insulating mixture present in liquid form is not homogeneous.

[0007] Since an electrical transformer is insulated by means of an insulating mixture in the gaseous phase, it is necessary to vaporize the liquid mixture.

[0008] A non-homogeneous insulating mixture in the liquid phase will not be homogeneous in the gas phase. In order to make the liquid phase homogeneous, the insulating mixture must be in a supercritical state. The supercritical state is a well-known phenomenon that appears at- Above the critical pressure and temperature of the insulating mixture, there is only one phase: gas or fluid. Below this critical pressure and temperature, the insulating mixture exists in two states: vapor and liquid, forming vapor-liquid equilibrium (VLE). Above the critical pressure and temperature, there is only one phase: gas or fluid. The mixture is therefore homogeneous in its supercritical state.

[0009] With reference to [Fig. 1], it is known to use a refilling system 103 connected, on the one hand, to a pressure drum 100 and, on the other hand, to the electrical transformer 9. The refilling system 103 includes a heating device 131 configured to heat the pressure drum 100 externally and allow its homogenization before being transferred to the electrical transformer 9. Such a refilling system 103 is bulky, energy-intensive, and expensive. Optionally, the refilling system 103 may include a mixing device 132.

[0010] To heat the 100-liter pressure drum, it has been proposed to place the drum in a heating chamber or to use a thermal belt surrounding it. The electrical consumption for external heating of the 100-liter pressure drum is significant due to substantial heat loss. In practice, the heating time is particularly long. Heating a 500-liter pressure drum requires a 380-volt three-phase power supply and a heating period of several hours, requiring an operator to work at least two days. Furthermore, it is crucial that the heating process be carried out meticulously; otherwise, the dielectric properties of the insulating mixture are severely compromised.Furthermore, heating the insulating mixture to over 30°C in the 100 pressure drum requires the drum itself to be heated to a high temperature, which presents a risk of burns for operators. From a regulatory standpoint, a 100 pressure drum can be used between -20°C and 65°C.

[0011] The invention thus aims to eliminate at least some of these drawbacks. PRESENTATION OF THE INVENTION

[0012] The invention relates to a pressure drum for storing an insulating mixture for an electrical transformer, the pressure drum comprising a chamber configured to receive the insulating mixture, the chamber comprising a wall defining an internal volume.

[0013] The invention is remarkable in that the pressure drum includes a heating device comprising at least one electric heating resistance positioned in the enclosure, the heating device being configured to heat the insulating mixture internally in order to make it homogeneous and allow the filling of an electrical transformer.

[0014] Thanks to the invention, the insulating mixture is heated internally rather than externally as in the prior art. This avoids heating the enclosure wall, which would result in heat loss and a risk of burns for operators. The heating is thus integrated, which is more practical, more economical, safer, and faster.

[0015] In one aspect, the electric heating element is in the form of an immersion heater. An immersion heater accelerates heating by increasing the heat exchange surface area.

[0016] According to one aspect, the enclosure comprising a top opening, the electric heating element includes a mounting flange connected to the top opening. This allows for convenient mounting while allowing the electric heating element to extend along the axis of the enclosure.

[0017] According to one aspect, given the enclosure's height, the electric heating element has a length greater than 50% of the enclosure height. This length allows for heating of both the liquid and gaseous phases of the insulating mixture. The longer the electric heating element, the larger the heat exchange surface area.

[0018] According to one aspect, the heating device is configured to be powered by a single-phase voltage, preferably below 250V. Since the heating is internal, energy requirements are lower and power consumption is reduced. This allows for the use of an electrical transformer in locations without a high-power power supply.

[0019] According to one aspect, the heating device includes at least one temperature sensor. Such a temperature sensor makes it possible to conveniently control the temperature of the mixture to ensure the proper homogeneity of the insulating mixture and also to monitor any safety risks.

[0020] According to one aspect, the heating device includes at least one upper temperature sensor positioned at the upper end of the electric heating element. This allows monitoring of the temperature of the gaseous phase of the insulating mixture. Heat exchange between the gaseous phase and the electric heating element is less significant than between the liquid phase and the electric heating element. Thus, a greater temperature rise in the electric heating element will occur in the gaseous phase; the upper temperature sensor serves as a safety measure to prevent an excessive temperature rise in the electric heating element.

[0021] According to one aspect, the heating device includes at least one lower temperature sensor positioned at one lower end of the heating element. This allows the temperature of the liquid phase of the insulating mixture to be monitored. If the temperature is excessive, the heating is stopped.

[0022] According to one aspect, the heating device includes a control unit configured to provide regulated heating up to a target temperature, preferably between 31°C and 65°C. This target temperature is reduced, thereby limiting electrical consumption and eliminating any risk of scalding while ensuring a homogeneous mixture.

[0023] According to one aspect, the pressure drum comprises at least one distribution line, fluidly connected to the enclosure, configured to distribute a liquid phase of the insulating mixture and at least one distribution line, fluidly connected to the enclosure, configured to distribute a gaseous phase of the insulating mixture.

[0024] In one aspect, the enclosure has a capacity of between 100L and 1000L. This allows the pressure drum to be transportable. This contrasts with fixed installations.

[0025] According to one aspect, the heating device includes at least one pressure sensor configured to measure the pressure in the enclosure. If the pressure is excessive, the heating is stopped.

[0026] According to one aspect, the pressure drum comprises a plurality of horizontal guides configured to allow the pressure drum to be transported with a pallet jack or forklift.

[0027] A method for filling an electrical transformer with an insulating mixture using a pressure drum as described above is also presented, the chamber of the pressure drum being filled with an insulating mixture comprising a plurality of components in determined proportions, the method comprising steps consisting of: • Activate the heating device to heat the insulating mixture inside the enclosure to form a homogeneous insulating mixture and • Fill the electrical transformer with the homogeneous insulating mixture. PRESENTATION OF THE FIGURES

[0028] The invention will be better understood upon reading the following description, given by way of example, and referring to the following figures, given by way of non-limiting examples, in which identical references are given to similar objects.

[0029] Fig. 1 is a schematic representation of a system for recharging an electrical transformer with an insulating mixture stored in a pressure drum according to the prior art.

[0030] Fig. 2 is a schematic representation of recharging an electrical transformer with an insulating mixture stored in a pressure drum according to the invention.

[0031] Fig. 3 is a schematic representation of a pressure drum according to one embodiment of the invention.

[0032] Fig. 4 is a schematic representation of the components of the insulating mixture in the pressurized drum before heating.

[0033] Fig. 5 is a schematic representation of the components of the insulating mixture in the pressurized drum after heating.

[0034] It should be noted that the figures set out the invention in detail to implement the invention, said figures being of course able to serve to better define the invention where appropriate. DETAILED DESCRIPTION OF THE INVENTION

[0035] With reference to [Fig.2], the invention relates to a pressure drum 1 for storing an insulating mixture M for an electrical transformer 9. The insulating mixture M is electrically insulating and has a dielectric effect.

[0036] Preferably, the insulating mixture M comprises a plurality of components in predetermined proportions. The insulating mixture M is, for example, a substitute for SF6 comprising a mixture of C4F7N, CO2 and O2 in predetermined proportions.

[0037] With reference to [Fig. 3], the pressure drum 1 comprises a vertically extending enclosure 2. It is understood that the enclosure 2 could also extend horizontally. The enclosure 2 is configured to receive the insulating mixture M, the enclosure 2 comprising a wall 20 defining an internal volume 21. The invention applies to a pressure drum 1 that is inherently transportable. The enclosure 2 has a capacity of between 100 L and 1000 L. The pressure drum 1 is preferably approved for dangerous goods (ADR). Optionally, the pressure drum 1 is insulated.

[0038] In enclosure 2, the insulating mixture M comprises, in the lower part, a liquid phase ML and, in the upper part, a gaseous phase MG. The liquid phase ML and the gaseous phase MG are separated by an interface INT as illustrated in [Fig.3].

[0039] The pressure drum 1 includes a distribution line 61, fluidly connected to the enclosure 2, configured to distribute the liquid phase ML of the insulating mixture M and a distribution line 62, fluidly connected to the enclosure 2, configured to distribute the gaseous phase MG of the insulating mixture M. It is understood that the pressure drum 1 could include several lines 61 and / or 62.

[0040] Preferably, the pressure drum 1 comprises a plurality of horizontal guides 7 configured to allow the pressure drum 1 to be transported with a pallet jack or forklift. The horizontal guides 7 are preferably positioned at the bottom of the pressure drum 1.

[0041] As illustrated in [Fig.3], the pressure drum 1 is notable in that it includes a heating device 3 comprising at least one electric heating resistance 4 positioned in the enclosure 2. The heating device 3 is configured to heat the insulating mixture M internally in order to make it homogeneous and allow the filling of an electric transformer 9.

[0042] As will be shown in detail later, such a heating device 3 allows the insulating mixture M to be heated internally, which limits heat loss and allows for more economical, faster, and safer heating. It is no longer necessary to heat the wall 20 of the enclosure 2 to a high temperature as in the prior art.

[0043] With reference to [Fig. 3], the electric heating element 4 is in the form of an immersion heater. The housing 2 includes a top opening 22, and the electric heating element 4 includes a mounting flange 40 connected to the top opening 22. This advantageously allows the electric heating element 4 to extend vertically within the housing 2 in order to maximize its surface contact with the insulating mixture M. This accelerates heating.

[0044] According to one aspect, the enclosure 2 has an enclosure height H2. The electric heating element 4 has a length L4 greater than 50% of the enclosure height H2. Preferably, the length L4 is between 70% and 100% of the enclosure height H2. This allows for faster heating by maximizing surface contact with the insulating mixture M.

[0045] According to one aspect, the heating device 3 comprises a control unit 5 configured to provide regulated heating up to a target temperature Te, preferably between 31°C and 65°C. Unlike prior art heating devices that required very high target temperatures to heat the insulating mixture M, the heating device 3 provides efficient heating while maintaining a low target temperature Te, since the heating is carried out inside the enclosure 2 and not outside, as in the prior art. This reduces power consumption.

[0046] According to one aspect, again with reference to [Fig. 3], the heating device 3 comprises an upper temperature sensor 52 positioned at an upper end 4A of the electric heating element 4 and a lower temperature sensor 51 positioned at a lower end 4B of the electric heating element 4. This advantageously allows the temperature of the gaseous phase TG at the upper end 4A to be measured, on the one hand, and the temperature of the liquid phase TL at the lower end 4B. This allows for the precise determination of the heating rate of the insulating mixture M, thus preventing overheating. The heating system is therefore redundantly protected.

[0047] Preferably, the heating device 3 includes at least one pressure sensor 6 configured to measure the pressure P2 in the enclosure 2. This allows for the detection of any suppression related to overheating. In this example, with reference to [Fig. 3], the pressure drum 1 includes a safety valve 8 to release the insulating mixture M if the pressure P2 exceeds a predetermined safety threshold.

[0048] In practice, the control unit 5 of the heating device 3 implements a control algorithm which controls the activation of the electric heating resistance 4 as a function of the setpoint temperature Te, the temperature measurements TG, TL and the pressure measurement P2. Thus, any risk of overheating or overpressure can be avoided.

[0049] Preferably, the heating device 3 is configured to be powered by a single-phase voltage below 250V, preferably at 220V or 230V. For this purpose, the heating device 3 includes an electrical connection socket 31 suitable for removably connecting to a power source. This allows for a convenient power supply that does not require a high-capacity electrical installation.

[0050] With reference to [Fig. 2], a method for filling an electrical transformer 9 with an insulating mixture M using a pressure drum 1 is schematically represented. With reference to [Fig. 4], prior to heating, the chamber 2 of the pressure drum is filled with an insulating mixture M comprising a plurality of components in predetermined proportions. As illustrated in [Fig. 4], at room temperature, the insulating mixture M is not homogeneous.

[0051] The heating device 3 of the pressure drum 1 is first connected to a 220V or 230V power supply. The process includes a step of activating the heating device 3 so as to heat the insulating mixture M in the chamber 2 in order to form a homogeneous insulating mixture M*.

[0052] With reference to [Fig. 3], upon activation, the electric heating element 4 heats the insulating mixture M by heating both the liquid phase ML and the gaseous phase MG. Preferably, the control unit 5 implements a heating time control algorithm to reach the target temperature Te, for example, 40°C. If the measured temperatures TG, TL or the pressure measurement P2 exceed predetermined safety thresholds, the heating element 3 is deactivated to ensure optimal safety.

[0053] After heating, the insulating mixture M is in a supercritical (gaseous) state and the components are homogeneously mixed to form a homogeneous insulating mixture M* as illustrated in [Fig. 5]. The homogeneous insulating mixture M* can be distributed in a practical way, without risk of altering the proportions of the components and, therefore, modifying its electrical properties.

[0054] The process includes a step of filling the electrical transformer 9 with the homogeneous insulating mixture M*, via the gas phase line 62. The properties of the insulating mixture M were not affected during filling. No special filling equipment is required, which simplifies implementation. The pressure drum 1 is preferably fluidly connected to the electrical transformer 9 before heating, but it can, of course, be connected afterward.

[0055] The operational benefit is significant. Electricity consumption is reduced since only the insulating mixture M is heated internally. It is not necessary to heat the walls 20 as in the prior art, which significantly increased heat loss. Furthermore, high-temperature heating was required, posing a risk of burns to the operator. Advantageously, the temperature of the pressure drum 1 always remains below 50°C, which complies with regulatory requirements.

[0056] It is therefore no longer necessary to use a charging system which is expensive and difficult to implement logistically for filling electrical transformers.

Claims

Demands

1. Pressure drum (1) for storing an insulating mixture (M) for an electrical transformer (9), the pressure drum (1) comprising • an enclosure (2) configured to receive the insulating mixture (2), the enclosure comprising a wall (20) defining an internal volume (21), • a heating device (3) comprising at least one electric heating element (4) positioned in the enclosure (2), the heating device (3) being configured to heat the insulating mixture (M) internally to make it homogeneous and allow the filling of an electrical transformer (9).

2. Pressure drum (1) according to claim 1 in which the enclosure (2) includes a top opening (22), the electric heating element (4) includes a mounting flange (40) connected to the top opening (22).

3. Pressure drum (1) according to any one of claims 1 to 2, wherein the enclosure (2) having an enclosure height (H2), the electric heating resistance (4) has a length (L4) greater than 50% of the enclosure height (H2).

4. Pressure drum (1) according to any one of claims 1 to 3, wherein the heating device (3) is configured to be powered at a single-phase voltage, preferably less than 250V.

5. Pressure drum (1) according to any one of claims 1 to 4 wherein the heating device (3) comprises at least one temperature sensor (51, 52).

6. Pressure drum (1) according to claim 5 in which the heating device (3) comprises at least one upper temperature sensor (52) positioned at an upper end (4A) of the electric heating resistance (4).

7. Pressure drum (1) according to any one of claims 5 to 6 in which the heating device (3) comprises at least one lower temperature sensor (51) positioned at a lower end (4B) of the electric heating resistance (4).

8. Pressure drum according to any one of claims 1 to 7 wherein the heating device (3) comprises a control unit (5) configured to provide regulated heating up to a target temperature (Te), preferably between 31°C and 65°C.

9. Pressure drum (1) according to any one of claims 1 to 8 comprising at least one distribution line (62), fluidly connected to the enclosure (2), configured to distribute a liquid phase of the insulating mixture (M) and at least one distribution line (61), fluidly connected to the enclosure (2), configured to distribute a gaseous phase of the insulating mixture (M).

10. Pressure drum (1) according to any one of claims 1 to 9, in which the enclosure (2) has a capacity between 100L and 1000L.

11. Pressure drum (1) according to any one of claims 1 to 10, wherein the heating device (3) includes at least one pressure sensor (6) configured to measure the pressure in the enclosure (2).

12. Pressure drum (1) according to any one of claims 1 to 11, wherein the pressure drum (1) comprises a plurality of horizontal guides (7) configured to permit the transport of the pressure drum (1) with a pallet truck.

13. A method of filling an electrical transformer (9) with an insulating mixture (M) by means of a pressure drum (1) according to any one of claims 1 to 12, the chamber of the pressure drum being filled with an insulating mixture (M) comprising a plurality of components in determined proportions, the method comprising steps of: • Activating the heating device so as to heat the insulating mixture (M) in the chamber (2) in order to form a homogeneous insulating mixture (M*) and • Filling the electrical transformer (9) with the homogeneous insulating mixture (M*).

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